Page 379 - Numerical Analysis and Modelling in Geomechanics

360 RESERVOIR COMPACTION, SUBSIDENCE AND WELL DAMAGE

Figure 11.12 Slip on the Tulare-diatomite unconformity computed in 1987 and the 1995
simulations.
displacement far from the casing is localized on a plane, shear deformations are
distributed over a finite length of casing in the detailed wellbore-scale model.
Logging tools have been developed or modified to measure the geometry of
shear-deformed casing. Such tools are capable of measuring the inclination of the
casing in the shear-damaged interval; this inclination has been referred to as the
“kink angle.” 42 The lateral offset of the casing from above to below the shear
interval can also be measured, and the geometry of the deformed casing can be
resolved. The computed deformed casing geometry is compared with
measurements from a casing log in Figure 11.16 (the nodes on the inner surface
of the casing are plotted). Shearing is distributed over about 7 feet of the casing
in both the model and the field measurements.
Shearing deformations are distributed over a finite length as a result of the
mechanical interaction between the stiff, strong casing and the soft, weak rock.
The rock fails or “flows” as it deforms around the casing, thus the casing